One type of engine currently used on commercial aircraft comprises a turbine engine assisted by a freestream fan or a ducted fan. The prop-fan engine consists of a turbine engine and a freestream propulsive fan mounted to either the forward or aft end of the turbine shaft. The turbofan engine consists of a turbine engine and a ducted propulsive fan mounted to either the forward or aft end of the turbine shaft. In either type of engine, the turbine of the engine absorbs energy from the expanding exhaust gases produced in the engine combustor to provide power to not only turn the engine compressor and its associated equipment, but also to deliver the torque for driving the propulsive fan. Thus, the propulsive forces for the aircraft are produced from the combined thrust of the turbine exhaust gases and the propulsive fan.
In order to convert the torque delivered to the engine shaft to which the prop-fan or ducted fan is mounted into thrust as efficiently as possible over a wide range of operating rpm, it is necessary to vary the pitch of the fan blades to minimize blade drag. A typical prop-fan or ducted fan includes a multiplicity of fan blades, usually from 6 to 12 for a prop-fan and up to 24 or more for a ducted fan, each of which is mounted to a radially extending arm of a fan hub which is mounted to the engine shaft for rotation therewith. In order to permit changes in blade pitch, each of the support arms is independently connected to the fan hub and is structurally independent from its counterparts. Each fan blade is retained within its support arm by means of a retention member, most commonly, a retention ring which is positioned about the shank of the fan blade in a bearing race on the disc arm. While this type of retention means has proven functionally most adequate, the fan blades are not readily removable. Thus, replacing fan blades is a labor intensive and time consuming task.
Accordingly, it is an object of the present invention to provide a retention arrangement for securing a blade to a support arm which permits ready and rapid removal and replacement of the blade.